Electronic performance support systems, as an emerging type of software environment, present many new challenges in relation to effective evaluation. In this paper, a global approach to a 'usage-orientated' evaluation methodology for software product is presented, followed by a specific example of the application of the methodology to electronic performance support systems. The usage-orientated evaluation methodology is characterised by: (a) its applicability throughout the life-cycle of a software product; (b) its blending of theoretical and practical aspects through a consistent focus on the eventual outcome, 'Will they use it?' ('use in practice'); (c) its use of a core evaluation instrument, the 'usage map', in various ways during the life-cycle of the product; and (d) its support of decision making for both those involved in the design process of the product and those representing its potential users.